Tilt focus method and mechanism for an optical drive

ABSTRACT

The present invention relates to a method and apparatus for dynamically positioning the objective lens in an optical disk drive to maintain focus despite loss of perpendicularity between the light beam and the information layer of the optical disk. Loss of perpendicularity may occur as a result of any number of factors, including irregularities in the manufacture of the disk, manufacturing tolerances and assembly of the disk drive components, bearing defect frequencies, shock and vibration. Failure to maintain perpendicularity may interference with the ability of the optical pick up unit of the drive to accurately read and write. The tilt focus mechanism of the present invention utilizes a rotary actuator that positions the objective lens in three dimensions relative to the surface of the optical disk. In one embodiment, a first voice coil motor positions the actuator generally in two dimensions parallel to the surface of the disk and a second voice coil motor positions the objective lens generally along an arcuate path orthogonal to the surface of the disk.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is related to U.S. patent application Ser. No.09/315,398, filed May 20, 1999, entitled “Removable Optical StorageDevice and System,” U.S. Provisional Application Ser. No. 60/140,633,filed Jun. 23, 1999, entitled “Combination Mastered and Writeable Mediumand Use In Electronic Book Internet Appliance,” U.S. patent applicationSer. No. 09/393,899, filed Sep. 10, 1999, entitled “Content DistributionMethod and Apparatus,” U.S. patent application Ser. No. 09/393,150,filed Sep. 10, 1999, entitled “Writeable Medium Access Control Using aMedium Writeable Area,” U.S. patent application Ser. No. 09/548,128,filed Apr. 12, 2000, entitled “Low Profile and Medium ProtectingCartridge Assembly,” U.S. patent application Ser. No. 09/560,781, filedApr. 28, 2000, entitled “Miniature Optical Disk for Data Storage,” andU.S. patent application Ser. No. 09/540,657, filed Mar. 31, 2000,entitled “Low Profile Optical Head,” all of which are incorporatedherein by reference in their entireties.

FIELD OF THE INVENTION

The present invention is directed generally to an optical disk drive andmore specifically to a method and mechanism for positioning an opticalpickup element in three dimensions relative to an optical disk. Theinvention may utilize single or multiple optical disks. In the case of asingle disk, the disk may be removable or non-removable.

BACKGROUND OF THE INVENTION

Optical disk drives are ideally suited for use in personal electronicdevices (PEDs). By way of example, optical disk drives may beadvantageously utilized in PEDs such as digital cameras, musicreproduction equipment, MP3 players, cellular telephones, dictatingequipment and personal digital assistants such as microcomputers. Inparticular, as compared to magnetic disk drives, optical disk drives aresuperior in terms of storage capacity, power consumption and datatransfer speed. As a result, they can be smaller in size and cost. To bepractical in PEDs, however, the optical drives need to be substantiallypocket sized (e.g., no more than about 100 mm in the largest dimension,but preferably no more than about 50 mm, and preferably having at leastone cross section no more than about 100 mm by about 50 mm, preferablyno more than about 75 mm by about 25 mm) and have a mass of no greaterthan about ⅓ kg.

Much of the development of optical disk data storage has centered aroundapparatus in which the read/write mechanism was configured to position aread/write beam at a desired radial location on the disk in asubstantially linear fashion (i.e., linear actuators). Typically, a sledcarrying an objective lens moves radially along a pair of rails betweenthe inside and outside diameter of a disk for course tracking purposes.A second mechanism or linkage is mounted in the sled and rotates theobjective lens in an arcuate path for fine tracking purposes. Furtherstructure also moves the objective lens orthogonally relative to thedisk surface for purposes of adjusting the focus of the light beam onthe data layer of the disk. While linear actuators have proved useful ina number of contexts, such as for reading/writing CDs and DVDs, thelocation and mass of the components in linear actuators has typicallyaffected performance parameters such as access time, data transferrates, and the like. In addition, linear actuators are relativelyhigh-friction devices and require precise track alignment. Linearactuators typically add substantial thickness to a read/write or drivedevice and generally do not scale well toward miniaturization. Also,linear actuators are typically unbalanced systems in that the mass ofthe components, including the objective tens, is not evenly distributedrelative to any pivot point. As a result, such actuators are highlysusceptible to shock and vibration. Thus, linear actuators have, ingeneral, found greatest use in applications where thickness, accesstime, bandwidth and power consumption are of less importance, andtypically are used in larger stationary devices where space for movingthe read/write head is available and the risk of shock or significantvibration is minimized.

Another factor affecting the size of an optical system is the size andshape of the light beam as it reaches the optical disk (the spot sizeand quality). Spot size and quality is, in turn, affected by a number offactors including, the size of the optical components, relative movementamong the optical components, the distance the light beam must traveland the format of the optical disk. Although a wide variety of systemshave been used or proposed, typical previous systems have used opticalcomponents (such as a laser source, lenses and/or turning mirrors) thatwere sufficiently large and/or massive that functions such as focusand/or tracking were performed by moving only some components of thesystem, such as moving the objective lens (e.g. for focus) relative to afixed light source. However, relative movement between opticalcomponents, while perhaps useful for accommodating relatively large ormassive components, presents certain disadvantages, including arelatively large form factor and the engineering and manufacturingassociated with establishing and maintaining optical alignment betweenmoveable components. Such alignment often involves manual and/orindividual alignment or adjustment procedures which can undesirablyincrease manufacturing or fabrication costs for a reader/writer, as wellas contributing to costs of design, maintenance, repair and the like.Accordingly, it would be useful to provide an optical head method,system and apparatus which can reduce or eliminate the need for relativemovement between optical components during normal operation and/or canreduce or eliminate at least some alignment procedures, e.g., duringreader/writer manufacturing.

In order to adequately miniaturize the mechanics associated with anoptical disk drive for use in a commercially acceptable PEDs, theoptical recording system's focus of the laser spot on the recording andplayback surface must be maintained to assure acceptable recording andplayback data integrity. In general terms, an objective lens directs alight beam to the optical disk and focuses the light beam into a conicalshape with the apex or focal spot occurring at the data layer within theoptical disk. Ideally, the conical beam is perpendicular to the surfaceof the disk, although, given irregularities in the manufacture of thedisk and its component layers (i.e. disk flatness), bearing defectfrequencies, and tolerances in the manufacture and assembly of themechanical components, as well as shock and vibrations imparted into thedisk drive during operation, perpendicularity between the disk surfaceand light beam is difficult to maintain. The distance between theobjective lens and the data layer determines the particularcharacteristics which the objective lens must possess. For example, thefarther the data layer of the disk is from the objective lens, thelarger the objective lens must be in order to focus the light beam intothe proper conical shape with the focal spot at or proximate to the datalayer. In turn, as the objective lens increases in size in order to formthe appropriately sized light beam, the other optical components mustalso increase in size in order to complement each other. Thus, forminiaturization purposes, it is critical to minimize this distancebetween the objective lens and the data layer on the disk.

A significant factor in reducing the distance between the objective lensand the data layer of the optical disk is the characteristics of thedisk itself. Optical disks used in consumer products today typicallyutilize second surface optical media as opposed to first surface opticalmedia. In the preferred embodiment of the present invention, the opticalmedium is first-surface media. Although it may be subject to more thanone definition, first-surface optical media refers to media in which theread beam during a read operation is incident on or impinges oninformation content portions of the first-surface optical media beforeit impinges on a substrate of the first-surface optical media. Theinformation content portions can be defined as portions of the opticalmedia that store or contain servo data, address data, clock data, userdata, system data, as well as any other information that is provided onthe optical media. The information content portions can be integral withthe substrate such as the case of a read-only media. The informationcontent portions can also be separately provided. In such a case, theinformation content portions can be, for example, an information layerof a writeable media Stated conversely, second-surface media can referto media in which the read beam is incident on the surface of the mediaor disk before it is incident on the information content portions.

A relatively thick and transparent outer layer or substrate ofsecond-surface optical medium makes read-only or read-write operationsrelatively insensitive to dust particles, scratches and the like whichare located more than 50 wavelengths from the information contentportions. Considering the cone angle of the light beam after the lightbeam passes through the objective lens, there is also little detrimentalchange to the shape or power of the light spot by the time it reachesthe information layer of this second-surface optical medium. On theother hand, the second-surface optical medium can be relativelysensitive to various optical aberrations. These optical aberrationsinclude: (1) spherical aberrations—a phase error causing rays atdifferent radii from the optic axis to be focused at different points;(2) coma—creating a “tail” on the recorded spot when the transparentlayer is not perpendicular to the optical axis; (3) astigmatism—creatingfoci along two perpendicular lines, rather than a symmetric spot; and/or(4) birefringence—different polarizations of light behave differentlybecause the read-only or read-write beam must propagate through arelatively longer distance before reaching the information layer, whenan aberration is created at the air/transparent layer interface. Thislonger distance is attributable to the thickness of the relatively thicktransparent substrate or layer. Compounding the unwanted birefringenceis the requirement that the read-write beam must also traverse thetransparent layer again after reflection.

Some or all of the aberrations arising from the presence of the thicktransparent layer can, at least theoretically, be partially compensatedfor by using a suitable focus mechanism. However, such a focusmechanism, including the optical elements thereof, tends to be large insize and, concomitantly, increases the cost of the system. Additionally,such a focus mechanism typically can only provide compensation for asingle, pre-defined thickness of the layer. Because there are likely beto spatial variations in the thickness or other properties of thetransparent layer, such compensation may be less than desired at somelocations of the medium.

Another drawback associated with second-surface optical media is thatthe optical requirements of such media are substantially inconsistentwith the miniaturization of the disk drive and optical components forsuch media. As will be appreciated by reference to FIG. 1A, a longerfocal length “f” is required for an optical system that will readinformation from or write information onto second-surface media This isdue to the relatively thick transparent layer “T” through which theradiation must pass to access the recording or data layer “D.” Toprovide the longer focal length a larger beam cone is required which, inturn, requires larger optical components (e.g., objective lens “O”).Moreover, the relatively long optical path through the thick transparentlayer to the data layer and back through the transparent layer afterreflection significantly decreases laser power efficiency in comparisonto a medium without the transparent layer. In comparison, as shown inFIG. 1B, a shorter focal length “f” can be achieved by utilizing firstsurface recording instead of second surface recording. Importantly, asmaller focal distance “f” allows use of a smaller objective lens “O.”This in turn allows the other optical components to be reduced in sizethereby facilitating overall miniaturization.

To date, rotary actuators have not provided a solution tominiaturization in optical disk drives either. Like linear actuatorsystems, rotary actuator systems are subject to the same problemscreated by imperfections in the manufacture of disks, mechanicaltolerances in the manufacture and assembly of the actuator arm andspindle, bearing defect frequencies, shock and vibration, among others.As a result, the data surface may be out of focus at any point in time,creating errors in reading from or writing to the disk. As statedearlier, optical drives have attempted to address this problem by movingthe objective lens orthogonal to the ideal or presumed plane of the disksurface to change its focal length, and thereby attempt to maintainfocus. This methodology has limited effectiveness. For example, inlarger disks, such as DVDs and CDs, errors or fluctuations arecompounded as the objective lens moves toward the outer diameter of thedisk. Thus, in order to try to maintain focus, the objective lens isrequired to move a greater distance away from or toward the disk surface(in the Z direction). However, the necessary range of movement in aminiaturized system would likely be constrained by space limitationsand/or physical limits purposefully placed in the drive to limitmovement. In unbalanced systems in particular, such physical limits arerequired to prevent linkages from moving past their elastic limits,primarily due to external shock.

SUMMARY OF THE INVENTION

The focus mechanism of the present invention solves many of theminiaturization problems associated with previous optical disk drivesystems. The present invention comprises a rotary actuator having atracking arm for movement of an optical pick up unit generally parallelto the disk surface and a focus arm for movement generally perpendicularto the disk surface. The focus arm may be balanced or unbalanced,although a balanced system is preferred in order to best handle shockand vibration. The optical pick up unit is supported at the distal endof the focus arm. In the preferred embodiment, the optical pick up unitincludes a light source, such as a laser, an objective lens fordirecting the light beam to the recording/playback surface of the diskand intermediate optical components such as turning mirrors and focusinglenses. The light beam is folded utilizing turning mirrors to achieve alength that is compatible with a chosen objective lens. The opticalpickup unit achieves further miniaturization when used in combinationwith media utilizing first surface data, although it will also work withsecond surface media. In the context of first surface data, theobjective lens can be smaller because the information containing portionor data layer is closer to the objective lens which allows use of a lenswith a shorter focal length.

The tilt focus method of the present invention also introduces anout-of-perpendicular condition for the laser beam for purposes ofmaintaining the focus of the light beam on the data layer of the disk.Rotation of the focus arm relative to the tracking arm moves or pivotsthe focus arm which also moves the optical pick up unit, including theobjective lens. In general terms, the optical pick up unit will move inan arcuate or curved path toward or away from the surface of the disk,although the directional component of movement orthogonal to the disksurface is substantially greater than the directional component ofmovement parallel to the disk surface. This is true for each of theembodiments described herein, except one, even though the magnitude ofmovement in each of the component directions may vary among embodiments.In the third principal embodiment described herein, the optical pick upunit does not move in an arcuate path. For purposes of this patent,however, the terms perpendicular or substantially perpendicular will beused to refer to movement of the optical pick up unit in eachembodiment.

By dynamically adapting the position of the objective lens duringoperation of the drive, the system can respond to variations in therelative position of the data layer caused by imperfections in themanufacture of the disk, manufacture and assembly tolerances ofcomponent parts, bearing defects, spindle motor run out, shocks,vibrations and other conditions that cause misalignment of the lightbeam relative to data on the disk. In this manner, the present inventionwill overcome conditions that could otherwise result in read/writeerrors.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross-sectional schematic view of a linear actuator andlight beam focused on a non-first surface data layer.

FIG. 1B is a cross-sectional schematic view of a linear actuator andlight beam focused on a first surface data layer.

FIG. 2 is a three-quarter perspective view of an optical disk drive ofthe present invention.

FIG. 3 is a three-quarter perspective view of a first embodiment of atilt focus mechanism of the present invention.

FIG. 4 is an exploded view of the component pieces of the tilt focusmechanism shown in FIG. 3.

FIG. 5 is a three-quarter perspective view of the tracking arm of thetilt focus mechanism shown in FIG. 3.

FIG. 6 is a three-quarter perspective view of the focus arm of the tiltfocus mechanism shown in FIG. 3.

FIG. 7 is a three-quarter perspective view of the tracking arm and focusarm of the tilt focus mechanism shown in FIG. 3.

FIG. 8 is a cross-sectional view of the tilt focus mechanism shown inFIG. 3.

FIG. 9 is a three-quarter perspective view of the flex circuit, opticalpick up unit and heat sink of the tilt focus mechanism of FIG. 3.

FIG. 10 is a cross-sectional view of a disk drive showing the tilt focusmechanism of FIG. 3, with the objective lens in a normal positionrelative to the optical disk.

FIG. 11 is a cross-sectional view of an optical disk drive containingthe tilt focus mechanism of FIG. 3, further showing the objective lenspivoted 0.6 degrees closer to the optical disk.

FIG. 12 is a cross-sectional view of an optical disk drive containingthe tilt focus mechanism of FIG. 3, further showing the objective lenspivoted 0.6 degrees away from the optical disk.

FIG. 13 is a three-quarter perspective view of a tracking arm and focusarm of a second embodiment of the tilt focus mechanism of the presentinvention.

FIG. 14 is an exploded perspective view of the tracking arm of theembodiment shown in FIG. 13.

FIG. 15 is an exploded perspective view of the focus arm of the tiltfocus mechanism shown in FIG. 13.

FIG. 16 is a three-quarter perspective view of a third embodiment of thetilt focus mechanism of the present invention.

FIG. 17 is an exploded view of the tilt focus mechanism shown in FIG.16.

FIG. 18 is a three-quarter perspective view of the tracking arm of thetilt focus mechanism shown in FIG. 16.

FIG. 19 is a three-quarter perspective view of the focus arm of the tiltfocus mechanism shown in FIG. 16.

FIG. 20 is a three-quarter perspective view of the fine actuator of thetilt focus mechanism shown in FIG. 16.

FIG. 21 is a three-quarter perspective view of the flex circuit of thetilt focus mechanism shown in FIG. 16.

FIG. 22 is a three-quarter perspective view of the suspension assemblyfor the tilt focus mechanism of the embodiment shown in FIG. 16.

FIG. 23 is a three-quarter perspective view of a fourth embodiment ofthe tilt focus mechanism of the present invention.

FIG. 24 is an exploded view of the tilt focus mechanism shown in FIG.23.

FIG. 25 is a three-quarter perspective view of the tracking arm andfocus arm of the tilt focus mechanism shown in FIG. 23.

FIG. 26 is a three-quarter perspective view of the flex circuit, opticalpick up unit and heat sink of the tilt focus mechanism shown in FIG. 23.

FIG. 27 is an exploded perspective view of an alternative embodiment ofthe actuator arm of FIG. 23.

FIG. 28 is an elevated plan view of the embodiment of FIG. 27.

FIG. 29 is an elevated side view of the embodiment of FIG. 27.

FIG. 30 is a three-quarter perspective view of a fifth embodiment of thetilt focus mechanism of the present invention.

FIG. 31 is a three-quarter exploded view of the components of the tiltfocus mechanism shown in FIG. 30.

FIG. 32 is a three-quarter perspective view of the tracking arm of thetilt focus mechanism shown in FIG. 30.

FIG. 33 is a three-quarter perspective view of the focus arm of the tiltfocus mechanism shown in FIG. 30.

FIG. 34 is a three-quarter perspective view of the flex circuit, opticalpick up unit and heat sink of the tilt focus mechanism shown in FIG. 30.

FIG. 35 is a cross-sectional view of the tilt focus mechanism shown inFIG. 30.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Turning to FIG. 2, a first embodiment of the tilt focus mechanism 10 isshown within the housing 12 of an optical drive 14. The housing 12includes a base plate 16 having an aperture 18 for receiving a spinmotor (not shown) and a slot 20 to receive a diskette containing anoptical disk (not shown). The cover plate has been removed. A disketteis inserted into the slot 20 and engages the spin motor positioned inaperture 18. An optical pick up unit 22 is positioned at the distal endof the tilt focus mechanism 10 and directs a light beam (not shown),such as a laser, to the optical disk which is spinning at a rapid rate.The light beam may be used to write information to the disk or may beused to read information resident on the disk. Because information isstored on the disk in tracks, typically concentrically arranged, theoptical pick up unit (OPU) 22 must be able to traverse the surface ofthe disk from the inside to the outside diameter in order to access theinformation formatted on the disk, whether in tracks or not. Toaccomplish this, the tilt focus mechanism 10 moves in three directionsrelative to the surface of the optical disk. Generally, the tilt focusmechanism 10 moves laterally across the disk surface for trackingpurposes, which can be defined as the X-Y plane for conveniencepurposes, and it also moves toward and away from the disk surface forfocusing purposes, which can be defined as the Z direction forconvenience purposes. In this manner, as explained in greater detailbelow, the tilt focus mechanism 10 can compensate for imperfections inthe optical media and read and write data to and from the optical diskmore accurately and faster than existing optical drives or magneticdrives.

As shown in FIGS. 3-8, a first embodiment of the tilt focus mechanism 10comprises a tracking arm 24 and a focus arm 26 disposed on the distalend of the tracking arm 24. Rotary motion is imparted to the trackingarm 24 by means of a voice coil motor (VCM) 28. More specifically, thetracking arm 24, shown separately in FIGS. 4 and 5, includes a centralbearing mounting bore 30 which receives a bearing cartridge 32. Thebearing cartridge 32 pivots about a fixed shaft 34 mounted between thetracing VCM return plate 36 and a voice coil motor magnet plate 38. Thetracking arm 24 further includes a wire coil 40 wound around a bobbin 42and adhered between a pair of rearwardly extending support arms 44, 46of the tracking arm 24 with an adhesive 48. By directing a currentthrough the wire coil 40 a magnetic field is created which interactswith the magnetic fields surrounding a pair of permanent trackingmagnets 50, 52 (shown in FIGS. 2 and 4), forcing the tracking arm 24 topivot about the shaft 34. It should be appreciated that the relativepositions of the permanent tracking magnets 50, 52 and the wire coil 40may be switched, with the coil 40 being stationary and the magnets 50,52 affixed to and moving with the tracking arm 24.

The focus arm 26 is mounted to the distal end of the tracking arm 24. Acounterweight 54 is typically affixed to the end of the tracking arm 24for purposes of counterbalancing about the shaft 34 the weight of thefocus arm 26 components on the opposite end of the tracking arm 24. TheOPU 22 is positioned on the distal end of the focus arm 26 between apair of support arms 56, 58. The purpose of the focus arm 26 is to movethe OPU 22 toward and away from the disk surface, in the Z direction. Afocus bearing assembly 60, mounted in the tracking arm 24, cooperateswith a shaft 62 to allow the focus arm 26 to rotate relative to thetracking arm 24 and the disk surface (i.e., in the Z direction). Theshaft 62 mounts in a pair of focus bearings 64 which, in turn, aremounted in a pair of pivot bearing supports 66, 68 in the focus arm 26.

Movement of the focus arm 26 relative to the tracking arm 24 is createdby a second voice coil motor (VCM) 70 (FIG. 4). As best seen in FIGS.5-8, a voice coil motor frame 72 is disposed at the forward end of thetracking arm 24. A pair of permanent magnets 74, 76 are mounted to theVCM frame 72. A focus coil 78, attached to the focus arm 26, ispositioned adjacent each of the permanent magnets 74, 76 with the centerarm 75 of the VCM frame 72 positioned in the open center area of thefocus coil 78. A spacer 80 may be included to optimize the position ofthe focus coil within the magnetic field created by the magnets 74, 76.By inducing a current in the focus coil 78, the focus arm 24 will pivotin the Z direction about the bearing assembly 60 relative to thetracking arm 24 (perpendicular to the surface of the disk). Acounterweight 82 is positioned at the distal end of the support arms 56,58 to balance the weight of the focus arm 26 and its components aboutthe shaft 62. It should be appreciated, however, that the relativeposition of the counterweight 82 and VCM 70 can be switched and the sameresults achieved. As a result of the balanced nature of the focus arm26, the VCM 70 can more easily adjust the position of the focus arm 26to focus the objective lens relative to the data surface of the disk. Inaddition, a key advantage of a balanced focus arm is its ability towithstand substantially larger shock and/or vibration forces than anunbalanced arm, without incurring a position error of the OPU 22relative to the data track.

A flex assembly or flex circuit 84 is affixed to the tracking arm andfocus arm to carry signals between the OPU 22 and appropriate processorsmounted on a printed circuit board and maintained in the housing 14 ofthe optical drive. Two different embodiments of the flex assembly 84 areshown in the drawings with this embodiment. As shown in FIGS. 3 and 9, afirst version of the flex circuit 84 is mounted to a bracket 86 affixedto the tracking arm 24 and is positioned along one side of the focus arm26, attaching to the underneath side of the focus arm 26 at its distalend. Alternatively, as shown in FIGS. 4 and 13, the flex circuit 84includes a rectangular bracket 86 which is positioned along both sidesof the focus arm 26. Both flex circuits 84 are designed to pivot in allthree directions of movement of the tilt focus mechanism 10 so as not toinhibit movement of the tilt focus mechanism. A heat sink 88 may beincluded in either version at the location where the OPU 22 attaches tothe flex circuit 84 to facilitate dissipation of beat generated by theoperation of the laser resident in the OPU 22.

In operation, servo information embossed or otherwise residing in thedata layer of the optical disk is monitored by the optical pick up unit22 and sent to appropriate processors over the flex cable 84. Based uponthe servo information, a processor (not shown) directs current to flowthrough coil 40 thereby creating a magnet field which induces movementof the tracking arm 24. The magnitude of the movement of the trackingarm is controlled by a processor. In this manner, the tracking arm 24can move the OPU 22 across the entire disk surface to move from onetrack to another or can minimally adjust the position of the OPU 22 tomaintain its position over a desired track. In other words, the trackingarm 24, including VCM 28, provides single stage tracking, i.e., bothcoarse and fine tracking.

In comparison, VCM 70 similarly adjusts the position of the OPU 22, butin a direction substantially perpendicular to the disk surface. Thisorthogonal component of this movement repositions the OPU 22 and itsobjective lens 90 to accommodate for disk flatness, variations inthickness in the disk layers, vibrations imparted into the system by thevarious motors, bearing defects, spindle motor run out and any otherimperfections that can lead to orthogonal misalignment of the OPU 22relative to the data tracks. For example, if the disk is created in sucha manner that the surface of the data layer fluctuates, the optical feedback to the processors can sense a change in the quality of the lightbeam and adjust the position of the OPU 22 using VCM 70 to correct formisalignment between the OPU 22 and the data layer. These adjustmentsare made dynamically to thereby decrease read/write errors and enhanceperformance. This adjustment is illustrated in FIGS. 10-12 which providea cross-sectional view of the tilt focus mechanism 10. FIG. 10 shows theoptical drive with the OPU 22 in its normal position, with the objectivelens 90 perpendicular to the surface of the disk “D.” FIG. 11 shows thefocus arm 26 repositioned such that the objective lens 90 is rotated 0.6degrees closer to the disk drive surface. As a result, the spacingbetween the objective lens 90 and the surface of the disk “D” isdecreased. Conversely, FIG. 12 shows the focus arm 26 repositioned withthe objective lens 90 0.6 degrees further away from the surface of thedisk “D.” Thus, the range of movement of the focus arm allows theobjective lens to maintain the light beam in a focused condition througha range of 1.2 degrees of movement thereby compensating forimperfections in the disk, the manufacture and assembly of the drivecomponents and external shock or vibration. It should be appreciatedthat the range of motion can be increased or decreased and that thepresent invention is not limited to this particular embodiment or rangeof motion. The size of the objective lens and its focal length are animportant factor in determining the amount of deviation fromperpendicular that any system can accommodate.

A variation of the foregoing embodiment is illustrated in FIGS. 13-15.In this embodiment, the VCM 70 utilizes a single permanent magnet 74. Asa result, the VCM frame 72 is smaller and lighter in weight. Because ofits lighter weight, the components of VCM 28 can be made smaller, asless torque is required to move the tilt focus mechanism 10. Morespecifically, the coil 40 and bobbin 42 may be made smaller, as can therear end of the tracking arm 24 supporting the VCM 28. With less mass,the counterweight 54 may also be smaller. A lighter weight and smallertilt focus mechanism 10 will achieve faster seek times and be moreaccurate. It will also be more compact, allowing furtherminiaturization. As with the previous embodiment, the general locationof the counterweight 54 and VCM 70 may be switched.

A third embodiment of the present invention is shown in FIGS. 16-22. Ingeneral, this embodiment includes a tracking arm 100 for course movementin the X-Y direction (parallel to the surface of the optical disk) and afocus arm 102 for fine tracking and for focus movement in the Zdirection (perpendicular to the disk surface). Thus, unlike the trackingarm 24 in the first two embodiments, tracking is accomplished by twostages rather than one. Like the tracking arm 24 in the first twoembodiments, the tracking arm 100 includes a bearing mount bore 104 forreceiving a bearing cartridge 106 which allows the tracking arm 100 topivot about a shaft 108 mounted between a tracking VCM return plate anda VCM magnet plate (not shown) of the optical drive. As should beappreciated by one skilled in the art, as an alternative, the shaft 108,in this embodiment or in any of the disclosed embodiments, may be fixedor stationary. A coil 110, wound around bobbin 112, is mounted between apair of support members 114, 116 at the rearward end of the tracking arm100, together with the counterweight 118. Magnets (not shown) arepositioned adjacent the coil 110 to form a voice coil motor to provide adirectional torque based upon the direction of current induced in thecoil 110 to move the tracking arm 100 relative to the surface of theoptical disk. It should be appreciated that the coil 110 may bestationary and the magnets may be positioned on the tracking arm 100 andmove with the tracking arm.

As best seen in FIG. 22, a suspension member 1 16 for supporting andpositioning the focus arm 102 comprises a cylindrical yoke 120 with twoshoulders 122, 124 extending outwardly from the yoke 120 in oppositedirections. The bearing assembly 106 fits inside the open center 126 ofthe yoke 120. Two pair of parallel support wires 128, 130 extend forwardfrom the suspension member 116 and terminate in a pair of frontsuspension mounts 132, 134. The support wires are enlarged at location136 (on the top and bottom surfaces of the yoke 120 and front suspensionmounts 132, 134) to facilitate stability and mounting between thesupport wires 128, 130, the yoke 120 and the forward suspension mounts132, 134. The focus arm 102 attaches to the front suspension mounts 132,134 and moves relative to the tracking arm 100 by a flexing of thesuspension wires 128, 130. Unlike the previously discussed embodiments,the present embodiment of the focus arm is unbalanced and, therefore,the focus arm 102 is subject to constant adjustment in order to maintainproper position. Such constant adjustment can drain power, particularlyif the weight of the components of the focus arm 102 is not minimized.Also, as an unbalanced member, it is more susceptible to misalignmenterrors created by shock or vibration. It may therefore be advisable toplace physical limits on the range of movement of support wires 128, 130to prevent them from moving past their elastic limit as a result of anexternal shock.

The focus arm 102 is moved relative to the tracking arm 100 by a hybridpair of voice coil type motors for both fine tracking and focus of theOPU 138 disposed at the end of the focus arm 102. A fine positioningactuator 140 is mounted between the front suspension mounts 132, 134.The fine actuator 140 includes a forward portion 142 with a cutout 144for housing the OPU 138. Fine tracking coils 146,148 are positionedbetween a pair of rear suspension arms 150, 152 of the fine actuator140. A focus coil 154 is positioned perpendicular to and within thecenter cavity 156, 158 of the fine tracking coils 146, 148. The finetracking coils 146, 148 and focus coil 154 coact with a pair ofpermanent magnets 160, 162 mounted to the tracking arm 100 (FIG. 18).The tracking arm 100 also includes a pair of VCM end returns 164, 166, acenter return 168 and a top plate 170 to create a magnet flux path inassociation with the hybrid voice coil motor. It should be appreciated,as a further alternative, that the coils 146, 148 and 156 could bemounted on the tracking arm 100 and the magnets 160 and 162 positionedon the fine actuator 140.

A flex circuit 172, shown in FIG. 21, provides a communication pathbetween the OPU 138 and the drive processors (not shown). In addition, aheat sink 174 may be added to facilitate removal of heat generated bythe laser within the OPU 138, as well as due to constant positioning ofthe fine actuator 140 for focusing, fine tracking and positioning of theobjective lens 176.

Applying a current to the fine tracking coils 146, 148 creates a forceon the focus arm 102 generally parallel to the disk surface, i.e. in theX-Y plane. This causes the support wires 128, 130 to bend sideways orlaterally, moving the OPU 138 and objective lens 176 generally parallelto the disk surface for fine tracking purposes. The flex circuit 172includes flat portions 178, 180 which accommodate bending in the X-Ydirection. Applying a current to the focus coil 154 will create a forcewhich moves the OPU 138 in a direction generally perpendicular to thedisk surface, i.e. in the Z direction. As compared to the otherembodiments described herein, the four bar linkage created by supportwires 128, 130 will tend to maintain the objective lens perpendicular tothe surface of the disk, rather than move the objective lens through anarcuate path. Flat portions 182, 184 of the flex circuit 172 bend inresponse to the force created by the focus coil 154. This movementallows the OPU 138 and objective lens 176 to move and maintain focus.

A fourth embodiment is disclosed in FIGS. 23-29. In general, thisembodiment comprises a single actuator arm 200 having a bearing boremount 202 which mounts to a bearing cartridge 204. The bearing cartridge204 is rotatably connected to a shaft 206 mounted between a tracking VCMreturn plate 208 and the cover or a similar cap structure (not shown).For coarse and fine tracking purposes, the actuator arm 200 moves in aconventional manner responsive to torque induced by VCM 210. The VCM 210comprises a coil 212 wound around a bobbin 214 placed within a pair ofarms 216 and 218 at the rear end of the actuator arm 200. Permanentmagnets 220 and 222, in cooperation with alternating current flowing inthe coil 212 and the return path provided by tracking VCM return plate208 and tracking VCM magnet plate 224, create the necessary torque topivot the actuator 200 about the shaft 206. The tracking VCM magnetplate 224 further includes an aperture 226 to provide clearance for theshaft 206 and bearing cartridge 204 to be secured between the VCM returnplate 208 and the cover. As will be appreciated, the components of theVCM 210 may be switched relative to each other such that the coil 212 isstationary and the magnets 220, 222 move with the actuator arm 200.

This embodiment utilizes an unbalanced focus structure. The focus arm228 of the actuator 200 includes a number of cutouts to lessen itsweight. Additionally, a slot 230 at the distal end is adapted to receiveOPU 232. Movement of the focus arm 228 of the actuator 200 in the Zdirection (perpendicular to the disk surface) is accomplished by anintegral flexure pivot 234 in the actuator 200 adjacent the bearing boremount 202. It should be understood, however, that the flexure need notbe integral to the actuator 200, but may be a separate piece or layer ina laminated composite structure. For example, the laminate structure maycomprise a carbon fiber composite upper layer 231, a metal center layerwhich includes the flexure 233, and a carbon fiber layer 235, as shownin FIGS. 27-29.

A focus VCM 236 acts to move the focus arm 228 of the actuator 200 (thefocus arm) in the Z direction. The VCM 236 comprises a coil 238 mountedto the focus arm 228. The shape of the coil 238 forms a channel 240which surrounds a permanent magnet 242 mounted within a VCM block 244.More specifically, the permanent magnet 242 is positioned within a slot246 formed in the VCM block 244. However, it should be appreciated thatthe shape of the coil may vary without effecting operation. For example,the coil 238 may be flat, i.e. two dimensional, rather than the threedimensional structure shown. The outer walls 248 and 250 of the VCMblock 244 create the return path for the magnetic flux, allowing thefocus arm 228 to move perpendicular to the surface of the disk as theoverall actuator arm 200 moves parallel to the surface of the opticaldisk. In addition, the coil 238 may be stationary and the magnet 242moves in association with the focus arm 228.

In this unbalanced embodiment, the voice coil motor 236 is positioned atthe center of percussion for the focus arm 228. It is advantageous tolocate the voice coil motor of the focus arm at, or as near as possibleto, the center of percussion for the overall focus arm in any unbalancedembodiments, if possible. In this manner, the force generated by thefocus arm VCM will minimize, or preferably eliminate, any detrimentalexcitation or resonance at the pivot point (i.e., flexure 234) for thefocus arm which could otherwise negatively affect focus. If the VCM 236were not positioned at or near the center of percussion, the forceplaced on the focus arm 228 by the VCM 236 could generate forces at thepivot point 234 which would interfere with the positioning of the focusarm, thereby potentially creating focus errors and, therefore, inhibitthe ability of the system to read and write. As used herein, the termcenter of percussion is understood to have the meaning set forth inMark's Standard Handbook for Mechanical Engineers (8 ^(th) ed.), whichis incorporated by reference.

A flex circuit 252, shown in FIGS. 23, 24 and 25, attaches along oneside of the actuator 200. A heat sink 254 is included to dissipate heatcreated by the laser (not shown) housed within the OPU 232. Thus, aswith the other embodiments, the objective lens 256 may be repositionedin the orthogonal direction relative to the disk surface in order tomaintain focus.

As will be appreciated, the integral flexure pivot 234 is only onestructure that allows for movement of the focus arm 228 in a directionperpendicular to the surface of the optical disk. First, the structureneed not be a single piece of material, but may be multiple or separatepieces. Pivoting may be provided by any number of known mechanisms,including but not limited to a ball bearing pivot, a jewel bearingpivot, a knife edge pivot, or a torsional shear member pivot or anyother type of pivot known by persons of skill in the art. While thevarious focus arms in the various embodiments illustrated herein can belengthened to achieve a greater range of motion, the objective is tominimize the angular change of the objective lens for any given range ofmotion of the focus arm in the Z direction. This embodiment allows forthe greatest range of movement of the objective lens with the leastperpendicularity error.

A fifth embodiment of the tilt focus mechanism 10 of the presentinvention is shown in FIGS. 30-35. As can be seen in FIG. 30, the tiltfocus mechanism includes a tracking arm 300 and a focus arm 302. Thetracking arm 300 is shown separately in FIG. 32 and the focus arm 302 isshown separately in FIG. 33, with the components of each shown in anexploded format in FIG. 31.

With reference to the tracking arm 300, a bearing bore mount 304receives a bearing cartridge 306 which, in turn, mounts to a shaft 308.The shaft 308 is seated between a tracking VCM return plate 310 and atracking VCM magnet plate 312. The rotational movement of the trackingarm 300 is provided by VCM 314, which includes a coil 316 wound around abobbin 318. Permanent magnets 320 and 322, in combination with the VCMmagnet plate 312, and return plate 310 and the coil 316, cause thetracking arm 300 to pivot about the shaft 308 and move the focus arm 302parallel to the surface of the disk for coarse and fine positioning ofthe OPU 324 relative to the tracks in the optical disk.

In this embodiment, the focus arm 302 is balanced. As can be appreciatedfrom FIG. 33, the VCM block 326, permanent magnet 328 and coil 330 arepositioned on the opposite side of the pivot point 332 for the focus arm302 than the OPU 324. The focus arm 302 moves in a directionperpendicular to the surface of the optical disk by rotation about shaft334. The ends of shaft 334 are seated in cutout portions 336 and 338formed in forward arms 340 and 342 of the tracking arm 300. The shaft334 passes through an aperture 344 formed in the VCM block 326. Bearings346 and 348 allow the focus arm 302 to pivot relative to the trackingarm 300. Rotational movement of the focus arm 302 about the shaft 334 iscaused by alternating the current path in coil 330 which creates amagnet field that interacts with the magnetic field of permanent magnet328. Depending upon the direction of the current in coil 330, a torqueis created relative to the field of the permanent magnet 328, causingthe focus arm 302 to move towards or away from the surface of theoptical disk.

The forward end of the focus arm 302 includes a pair of support arms 350and 352, which hold and support the OPU 324 containing objective lens356. A flex circuit 358 provides control signals to the OPU fromappropriate microprocessors (not shown). A heat sink 360 can be includedto assist dissipating heat generated by the laser (not shown) within theOPU 324.

While a few principal embodiments and certain alternative embodimentshave been shown and described, it will be apparent that othermodifications, alterations and variations may be made by and will occurto those skilled in the art to which this invention pertains,particularly upon consideration of the foregoing teachings. For example,the pivoting or rotation of the tracking arm and the focus arm may beprovided by a ball bearing pivot, jewel bearing pivot, knife edge pivot,flexure pivot, bushing pivot, split band pivot or any type of torsionalpivot such as a torsional shear member pivot or other type of structureknown to persons of skill in the art for achieving the desired relativemovement. In addition, it would be understood that the location of anypivot point of the focus arm could be changed, as could the location andarrangement of the voice coil motor components. For example, either themagnets or the coil could be stationary and the other move relative tothe stationary components. Additionally, the respective VCM magnets andcoils, on both the tracking arm and focus arm, can be alternativelypositioned on the same side of the rotational axis as the optical pickup unit or on the opposite side of the rotational axis as the opticalpick up unit for the respective arm. In doing so, however, it should beunderstood that this relative close proximity of multiple voice coilmotors may lead to cross coupling between the VCMs which can affect theperformance of the tracking arm and focus arm. In the present invention,this problem has been addressed by optimizing the various return pathstructures as shown in the illustrated embodiments. In particular, forthe specific embodiments disclosed herein, the return paths have beenselected, in part, to assist in directing the magnetic fields to theappropriate VCM and away from the other VCM. It is thereforecontemplated that the present invention is not limited to theembodiments shown and described and that any such modifications andother embodiments as incorporate those features which constitute theessential features of the invention are considered equivalents andwithin the true spirit and scope of the present invention.

1. An optical disk drive comprising: a housing including a base portion;an optical disk having information on at least one side; said opticaldisk mounted on a shaft for rotation; a rotary actuator including atracking arm and a focus arm having a first end and a second end, saidfirst end pivotally mounted to said base portion for positioning thesecond end relative to the surface of the disk; an optical pick up unitdisposed on said second end of said actuator, said optical pick up unitcomprising a light beam generating member, an objective lens and atleast one light beam directing member.
 2. The optical disk drive ofclaim 1, wherein said rotary actuator pivots about a shaft.
 3. Theoptical disk drive of claim 1, wherein said rotary actuator comprises aknife edge pivot.
 4. The optical disk drive of claim 1, wherein saidrotary actuator comprises a ball bearing pivot.
 5. The optical diskdrive of claim 1, wherein said rotary actuator comprises a jewel bearingpivot.
 6. The optical disk drive of claim 1, wherein said rotaryactuator comprises a flexure pivot.
 7. The optical disk drive of claim1, wherein said rotary actuator comprises a bushing pivot.
 8. Theoptical disk drive of claim 1, wherein said rotary actuator comprises asplit band pivot.
 9. The optical disk drive of claim 1, wherein saidrotary actuator comprises a torsional pivot.
 10. The optical disk driveof claim 1, wherein said rotary actuator moves in three dimensionsrelative to the surface of the disk.
 11. The optical disk drive of claim1, wherein said focus arm comprises a voice coil motor which issubstantially balanced relative to the axis of rotation for said focusarm.
 12. The optical disk drive of claim 1, wherein said focus armcomprises a voice coil motor which is unbalanced relative to the axis ofrotation for said focus arm.
 13. The optical disk drive of claim 1,wherein said tracking arm moves substantially parallel to the surface ofthe disk and said focus arm moves said optical pick up unit in adirection substantially perpendicular to the surface of the disk. 14.The optical pick up unit of claim 13, wherein said tracking armcomprises a voice coil motor having a moving magnet.
 15. The opticalpick up unit of claim 14, wherein said moving magnet is on the same sideof the rotational axis for said tracking arm as is said optical pick upunit.
 16. The optical pick up unit of claim 14, wherein said movingmagnet is on the opposite side of the rotational axis for said trackingarm as is said optical pick up unit.
 17. The optical pick up unit ofclaim 13, wherein said tracking arm comprises a voice coil motor havinga moving coil.
 18. The optical pick up unit of claim 17, wherein saidmoving coil is on the same side of the rotational axis for said trackingarm as is said optical pick up unit.
 19. The optical pick up unit ofclaim 17, wherein said moving coil is on the opposite side of therotational axis for said tracking arm as is said optical pick up unit.20. The optical pick up unit of claim 13, wherein said focus armcomprises a voice coil motor having a moving magnet.
 21. The opticalpick up unit of claim 20, wherein said moving magnet is on the same sideof the rotational axis for said focus arm as is said optical pick upunit.
 22. The optical pick up unit of claim 20, wherein said movingmagnet is on the opposite side of the rotational axis for said focus armas is said optical pick up unit.
 23. The optical pick up unit of claim13, wherein said focus arm comprises a voice coil motor having a movingcoil.
 24. The optical pick up unit of claim 23, wherein said moving coilis on the same side of the rotational axis for said focus arm as is saidoptical pick up unit.
 25. The optical pick up unit of claim 23, whereinsaid moving coil is on the opposite side of the rotational axis for saidfocus arm as is said optical pick up unit.
 26. The optical disk drive ofclaim 1, wherein said rotary actuator is a single stage for tracking.27. The optical disk drive of claim 1, wherein said rotary actuator is adual stage for tracking.
 28. The optical pick up unit of claim 12, wheresaid focus arm voice coil motor is positioned proximate the center ofpercussion of said focus arm.
 29. In an optical disk drive including ahousing having a base and cover, an optical disk mounted on a spindlefor rotation relative to said base, data resident on the optical disk, alight emitting source for generating a light beam to read data from andwrite data to the disk, and an actuator for positioning an objectivelens relative to the surface of the disk, the objective lens acting todirect the light beam to the disk, the improvement comprising: theactuator being a rotary actuator and the light emitting source and theobjective lens both positioned at the distal end of the rotary actuator;and said actuator including a first arm to position the objective lensin two dimensions substantially parallel to the surface of the opticaldisk, and a second arm mounted to said first arm to position theobjective lens in a third dimension substantially perpendicular to thesurface of said optical disk.
 30. The optical disk drive of claim 29further comprising a first pivot means for positioning said first armand a second pivot means for positioning said second arm.
 31. Theoptical disk drive of claim 30, wherein said first pivot means comprisesa voice coil motor.
 32. The optical disk drive of claim 31, wherein saidvoice coil motor comprises a moving magnet.
 33. The optical disk driveof claim 32, wherein said moving magnet is disposed on the same side ofthe rotational axis for the first arm as is said light source and saidobjective lens.
 34. The optical disk drive of claim 32, wherein saidmoving magnet is disposed on the opposite side of the rotational axisfor the first arm as is said light source and said objective lens. 35.The optical disk drive of claim 31, wherein said voice coil motorcomprises a moving coil.
 36. The optical disk drive of claim 35, whereinsaid moving coil is disposed on the same side of the rotational axis forthe first arm as is said light source and said objective lens.
 37. Theoptical disk drive of claim 35, wherein said moving coil is disposed onthe opposite side of the rotational axis for the first arm as is saidlight source and said objective lens.
 38. The optical disk drive ofclaim 30, wherein said first pivot means comprises one of the groupcomprising a ball bearing pivot, jewel bearing pivot, a knife edgepivot, a flexure pivot, a bushing pivot, a split band pivot, and atorsion pivot.
 39. The optical disk drive of claim 30 wherein saidsecond pivot means comprises a voice coil motor.
 40. The optical diskdrive of claim 39, wherein said voice coil motor comprises a movingmagnet.
 41. The optical disk drive of claim 40, wherein said movingmagnet is disposed on the same side of the rotational axis for thesecond arm as is said light source and said objective lens.
 42. Theoptical disk drive of claim 40, wherein said moving magnet is disposedon the opposite side of the rotational axis for the second arm as issaid light source and said objective lens.
 43. The optical disk drive ofclaim 39, wherein said voice coil motor comprises a moving coil.
 44. Theoptical disk drive of claim 43, wherein said moving coil is disposed onthe same side of the rotational axis for the second arm as is said lightsource and said objective lens.
 45. The optical disk drive of claim 43,wherein said moving coil is disposed on the opposite side of therotational axis for the second arm as is said light source and saidobjective lens.
 46. The optical disk drive of claim 30, wherein saidsecond pivot means comprises one of the group comprising a ball bearingpivot, a jewel bearing pivot, a knife edge pivot, a flexure pivot, abushing pivot, a split band pivot, a torsion pivot.
 47. The optical diskdrive of claim 29, wherein the data on the disk is ranged in track andsaid first arm comprises a single stage member for coarse and finetracking.
 48. The optical disk drive of claim 29, wherein the data onthe disk is arranged in track and said first arm comprises a dual stagemember for coarse and fine tracking.